1. Field of the Invention
The invention relates to a method for estimating the longitudinal speed of a motor vehicle with two driven wheels, from the rotational speeds of its four wheels.
2. Discussion of the Background
Most of the controlled systems of a vehicle, such as the braking system, the electric power assisted steering system and the system for controlling the four wheels when all four wheels are steered, need information regarding the longitudinal speed of the vehicle. This is generally estimated from the rotational speeds of the four wheels, as measured by sensors.
One of the technical problems of this estimating stems from the unrealistic “jumps”, that is to say speed gradients that are too great to correspond to an actual variation in the speed of the vehicle, whether under nominal circumstances or if there is an undetected failure of one or more of the wheel rotational speed sensors.
The current estimating methods, which are unable to give rise to large speed gradients, use a sensor that senses the longitudinal acceleration of the vehicle, as described for example in the CONTINENTAL TEVES Inc. American patent U.S. Pat. No. 6,792,803. However, a solution such as this is expensive because it adds a sensor to the vehicle.